The invention relates to a micromanipulator for producing a relative movement between itself and an object, whereby the micromanipulator has piezoelectric movement elements which are provided with end pieces.
Micromanipulators of this type are used to effect movement in scanning tunnel microscopes (STM) or scanning force microscopes or atomic force microscopes (SFM or AFM). Here the highest possible degree of precision is required for the movement of the sensing needle (tunnel tip) relative to the object to be investigated by the micromanipulator.
In DE 36 10 540 C2, a micromanipulator is described in which, for the support of the object to be investigated, a multiplicity of movement elements of piezoelectric materials are fastened on a base plate. The movement elements are so configured that they can effect micromovements of an object or object holder resting on the movement elements, e.g. translational movements and rotational movements, as well as a tilting of the object. The described micromanipulator is arranged for micromovement of the object with any optional micromovement. Perpendicular to the object plane, movements are effected only to the extent that they are permitted by the deformation of the piezoelectric materials by the applied electrical voltage.
In DE 38 22 504, a further development of the aforedescribed micromanipulator is disclosed. Ii it the movement elements are arranged on a part which is movable against the force of a spring relative to the base plate, whereby via the spring a micromovement of the order of magnitude of several tenths of a millimeter is effected perpendicular to the object plane while maintaining its basically horizontal orientation. A similar effect can be produced with the configuration of a micromanipulator according to DE 38 44 659 A1.
In FIG. 6 of this document an embodiment is disclosed in which the micromanipulator in an inverted arrangement is configured as a runner which extends above the piezoelectric movement elements on an object. The runner can be moved entirely translatorily or rotationally in a horizontal plane or in a plane tilted thereto at a small angle. With the aid of such a micromanipulator, even larger objects can be analyzed without detriment.
In DE 38 44 821 C2, a micromanipulator is disclosed in which the movement elements are provided with end pieces for the apparatus which are so mounted in axially extending bushings that friction forces between mutually bounding surfaces at end pieces and bushings hinder a movement of the support in the bushing. The frictional forces are so dimensioned that they on the one hand suffice to brace the object or the object holder and, on the other hand, by application of voltage functions to the piezoelectric material achieve a sliding of the end piece in the bushing in the axial direction. Thus by piezoelectric deformation the adhesion friction forces between end piece and bushing are eliminated and the relative movement is produced by inertia. In this configuration, the movement elements are perpendicular to the shaping or analysis plane for the micromovement and the macromovement of the object or object holder is utilized. In any case, the micromovements remain limited to a fraction of the length of the movement element.
A basic problem in the use of scanning probe microscopes (scanning tunnel microscopes and scanning force microscopes) resides in the fact that in the investigation of certain surface regions on a workpiece, a sample must be separated therefrom which contains the surface to be investigated. The sample is then introduced into the microscope apparatus. The separation can only be avoided in those particular cases in which the workpiece itself is very small or in an appropriate shape for investigation in the microscope apparatus. In many cases the need for taking a sample prevents microscopic investigation, for example, when the workpiece on objective grounds or because cost should not be damaged or because of its geometry is not capable of being introduced into the microscope apparatus as is the case, for example with an engine block, a bridge girder, etc.
Up to now, no scanning probe microscope or micromanipulator is known which is suitable for the investigation of optional locations on large immovable workpieces. This is because of one or more of the following reasons:
(i) The scanning probe microscope is not functionally suitable because of its excess sensitivity with respect to noise and vibration without special oscillation damping.
(ii) The scanning probe microscope requires the proximity of probe and sample and for the investigation of the sample, a certain sample orientation.
(iii) The scanning probe microscope does not structurally permit the approximation of a probe to an optional location of the sample on a workpiece with the requisite precision and closeness required in the scanning probe microscope.
Thus for scanning probe microscopes of the above described types, all three of the mentioned reasons are applicable.
Especially the sensitivity identified under (i) of the scanning probe microscope to noise and vibration is a basic problem in the use of all scanning probe microscopes. Thus the operation of variable temperature scanning probe microscopes of the above described types (compare Bott et a., xe2x80x9cDesign Principles of a variable temperature scanning tunneling microscopexe2x80x9d, Rev. Sci. Instrumen. 66 (8), August 1995, P. 4135 to 4139) is affected by the boiling of the coolant to a significant degree through vibration.
The application force between the object or the object holder with the sample and the microscope or of the runner on the object or the object holder has been only a result of the intrinsic weight. The application force is only small and gives rise, at the bearing points in the presence of environmental noise or vibration to relative movement between the micromanipulator and object or object holder (compare Behler et al, xe2x80x9cMethod to characterize the vibrational response of a beetle type scanning tunneling microscopexe2x80x9d, Rev. Sci. Instrum. 68 (1), January 1997, P. 124 to 128). To solve this problem, various possibilities have been proposed in this document, for example, the reduction of the possibility of introduction of the environmental noise by improved vibration insulation or the change in the configuration of the micromanipulator to increase the application force, e.g. by increasing the weight or by the use of a magnetic or electrostatic clamping of the microscope and object. As to how this can be achieved in detail, the document sheds no light. If the piezoelectric movement elements are loaded, the aforementioned problems are not resolved. The internal resonance frequency of the movement elements decreases sharply by loading and thus again gives rise to increased sensitivity of the scanning probe microscope to environmental noise and vibration.
The invention thus has as its object a micromanipulator of the type mentioned at the outset but of reduced sensitivity to environmental noise or vibration so that it can also be used at optional locations on a large object without requiring comminution of it.
This object is achieved in accordance with the invention in that the end pieces are magnetic or magnetizable. With end pieces configured in accordance with this feature, the application force can be significantly increased. To the extent that the end pieces are magnetic, it suffices that the object to be investigatedxe2x80x94or the object holderxe2x80x94be composed of a magnetizable material or have a magnetizable coating. If the end pieces are only configured to be magnetizable, it is necessary for increasing the application force that the object itselfxe2x80x94or the object holderxe2x80x94be magnetic. The advantage of the micromanipulator with the configuration according to the invention is that the piezoelectric material of the movement elements is not loaded by the increase in the application force since the application force increase is exclusively effected between the end pieces of the movement elements and the object or object holder. As a result there does not arise a reduction in the intrinsic resonance of the movement elements. Rather there is an increase in the intrinsic resonance because of the bond with the workpiece. This enables the micromanipulator to be used under normal environmental conditions without external vibration damping and in spite of it to obtain a high resolution of better than 1 nm on an optional object. The invention thus presents especially an improvement for all micromanipulators in the significant elimination of vibration or ambient noise or where an insulation from such detrimental influences is not possible.
The further advantage of the micromanipulator configured in accordance with the invention is that because of the great adhesive force between the micromanipulator and objectxe2x80x94or object holderxe2x80x94the function of the micromanipulator in any optional orientation is ensured and is no longer limited to a substantially horizontal orientation of the plane of the end pieces (and thus the object). This enables especially the micromanipulator to be operated at any optionally oriented location of a large object without comminuting it. This feature also enables objects to be transported in optional directions over macroscopic and structurally unlimited distances.
To the extent that the end pieces are of magnetic configuration, the invention provides that the end pieces be comprised at least partly of magnetic material. Alternatively, the end pieces can also be comprised at least partly of magnetizable material and that they be juxtaposed each with a respective magnet which magnetizes the end piece. For the magnets, permanent magnets or electromagnets can answer.
In a further feature the invention provides that the micromanipulator has an object holder which rests upon end pieces and is configured to be magnetic or magnetizable. Thus the object holder can be applied to an object or a part thereof. Such an object holder is concerned with very small workpieces which should be investigated. When the end pieces are magnetic, it suffices for the object holder to be comprised of a magnetizable material. If the end pieces are only magnetizable, the object holder should itself be magnetic to increase the application force between end pieces and object holder. The magnetic characteristics of the object holder can be obtained by means of permanent magnets or electromagnets.